void bootmain(void)
{
    //在bios打印 QUEST-OS
    short *p = (short *)0xb8000;
    *p++=81|0x700; //Q
    *p++=85|0x700; //U
    *p++=69|0x700; //E
    *p++=83|0x700; //S
    *p++=84|0x700; //T
    *p++=95|0x700; //-
    *p++=79|0x700; //O
    *p++=83|0x700; //S
}